Many marking technologies exist for creating marks or patterns on a substrate. The ink jet printing technology commonly known as “drop-on-demand” provides ink droplets (typically including a dye or a mixture of dyes) for impact upon a recording surface using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of a flying ink droplet that crosses the space between the printhead and the print media and strikes the print media. The formation of printed images is achieved by controlling the individual formation of ink droplets, as is required to create the desired image. Typically, a slight negative pressure within each channel keeps the ink from inadvertently escaping through the nozzle, and also forms a slightly concave meniscus at the nozzle, thus helping to keep the nozzle clean.
Activation of a pressurization actuator produces an ink jet droplet at orifices of a print head. Typically, one of two types of actuators is used including heat actuators and piezoelectric actuators. With heat actuators, a heater, placed at a convenient location, heats the ink causing a quantity of ink to phase change into a gaseous bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled. With piezoelectric actuators, an electric field is applied to a piezoelectric material possessing properties that create a mechanical stress in the material causing an ink droplet to be expelled. The most commonly produced piezoelectric materials are ceramics, such as lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
Conventional ink jet printers are disadvantaged in several ways. For example, in order to achieve very high quality images while maintaining acceptable printing speeds, a large number of discharge devices located on a printhead need to be frequently actuated thereby producing an ink droplet. While the frequency of actuation reduces printhead reliability, it also limits the viscosity range of the ink used in these printers. Typically, adding solvents such as water, etc. lowers the viscosity of the ink. The increased liquid content results in slower ink dry times after the ink has been deposited on the receiver, and this decreases overall productivity. Additionally, increased solvent content can also cause an increase in ink bleeding during drying which reduces image sharpness, negatively affecting image resolution and other image quality metrics. For receivers such as plain paper, excessive liquid can also lead to local mechanical buckling of the receiver.
Conventional ink jet printers are also disadvantaged in that the discharge devices of the printheads can become partially blocked and/or completely blocked with ink. In order to reduce this problem, solvents, such as glycol, glycerol, etc., are added to the ink formulation, which can adversely affect image quality. Alternatively, discharge devices are cleaned at regular intervals in order to reduce this problem. This increases the complexity of the printer.
Other technologies that deposit a dye onto a receiver using gaseous propellants are known. For example, E. Peeters et al., in U.S. Pat. No. 6,116,718, issued Sep. 12, 2000, disclose a print head for use in a marking apparatus in which a propellant gas is passed through a channel, the marking material is introduced controllably into the propellant stream to form a ballistic aerosol for propelling non-colloidal, solid or semi-solid particulate or a liquid, toward a receiver with sufficient kinetic energy to fuse the marking material to the receiver. A disadvantage of this technology is that the marking material and propellant stream are two different entities. When the marking material is added into the propellant stream in the channel, a non-colloidal ballistic aerosol is formed prior to exiting the print head. This non-colloidal ballistic aerosol, which is a combination of the marking material and the propellant, is thermodynamically not stable. As such, the marking material is prone to settling in the propellant stream which, in turn, can cause marking material agglomeration, leading to nozzle obstruction and poor control over marking material deposition.
Technologies that use supercritical fluid solvents to create thin films are also known. For example, R. D. Smith in U.S. Pat. No. 4,734,227, issued Mar. 29, 1988, discloses a method of depositing solid films or creating fine powders through the dissolution of a solid material into a supercritical fluid solution and then rapidly expanding the solution to create particles of the marking material in the form of fine powders or long thin fibers, which may be used to make films. C. Lee et al. in U.S. Pat. No. 4,923,720, issued May 8, 1990, disclose a liquid coating process and apparatus in which supercritical fluids, such as supercritical carbon dioxide, are used to reduce to application consistency viscous coating compositions to allow for their application as liquid sprays. In these disclosures the free-jet expansion of the supercritical fluid solution results in sprays with a shape that cannot be used to create high-resolution patterns on a receiver without a mask.
U.S. Pat. No. 6,752,484 entitled “Apparatus And Method of Delivering A Beam of A Functional Material To A Receiver” by R. Jagannathan et al. discloses a method and apparatus for delivering a solvent free marking material to a receiver wherein the discharge device is shaped to produce a collimated beam of the marking material with the fluid being in a gaseous state at a location beyond the outlet of the discharge device. Thus, this method describes delivering of marking materials in a manner such that it solves many of the drying related problems inherent to conventional, solvent based systems.
U.S. Pat. No. 6,971,739 entitled “Method And Apparatus For Printing” issued Dec. 6, 2005 by S. Sadasivan et al. describes a printhead for delivering marking material to a receiver includes a discharge device having an inlet and an outlet with a portion of the discharge device defining a delivery path. An actuating mechanism is moveably positioned along the delivery path. A material selection device has an inlet and an outlet with the outlet of the material selection device being connected in fluid communication to the inlet of the discharge device. The inlet of the material selection device is adapted to be connected to a pressurized source of a thermodynamically stable mixture of a fluid and a marking material, wherein the fluid is in a gaseous state at a location beyond the outlet of the discharge device.
U.S. Pat. No. 6,672,702 by S. Sadasivan et al. entitled “Method and Apparatus for Printing, Cleaning and Calibrating” describes a printing apparatus comprising: a pressurized source of a thermodynamically stable mixture of a compressed fluid and a marking material; a pressurized source of a compressed fluid; a material selection device having a plurality of inlets and an outlet, one of the plurality of inlets being connected in fluid communication to the pressurized source of compressed fluid and another of the plurality of inlets being connected in fluid communication to the thermodynamically stable mixture of the compressed fluid and the marking material; a printhead, portions of the printhead defining a delivery path having an inlet and an outlet, the inlet of the delivery path being connected in fluid communication to the outlet of the material selection device; and an actuating mechanism moveably positioned along the delivery path, wherein, the compressed fluid is in a gaseous state at a location beyond the outlet of the delivery path; and a cleaning station positioned relative to the printhead, wherein the printhead is moveable to a position over the cleaning station. This patent also includes a marking material measuring device useful for calibrating the amount of marking material being delivered to the substrate.
U.S. Pat. No. 6,595,630 by R. Jagannathan et al. entitled “Method And Apparatus For Controlling Depth of Deposition of a Solvent Free Functional Material In A Receiver” describes a method of delivering a functional material to a receiver comprising in order: providing a mixture of a fluid having a solvent and a functional material; causing the functional material to become free of the solvent; causing the functional material to contact a receiver having a plurality of layers and causing the functional material to penetrate and pass through the first layer of the receiver and penetrate a second layer of the receiver such that the second layer primarily contains the functional material.
For broad use applications, there is still a need to employ discharge devices that enable efficient mass manufacturing of printing systems that use compressed fluids based marking materials. Micro-machined devices are advantageous from that perspective although with shrinking dimensions come many challenges of material properties, ability to design and fabricate micro-machined structures to perform under high pressures, and operating without clogging of micro-nozzles. Micro Electro Mechanical Systems (MEMS) are used in many mass-market commercial devices such as accelerometers, pressure sensors, ink jet printer heads, and digital mirror arrays for projectors.
The ability to develop viable MEMS in any new area is to a large degree enabled and constrained by the set of materials and micro-machining processes from which a designer can select. Hitherto the vast majority of commercial MEMS have utilized the Complementary Metal Oxide Semiconductor (CMOS) and Very Large Scale Integration (VLSI) materials and process set. Details of such materials and processes are available in published literature including, for example, Introduction to Micro Fabrication by Sami Franssila, 2004, John Wiley and Sons, Ltd. So far, viable MEMS for printing with compressed fluids have not been disclosed. For such a system, in addition to known problems of nozzle shape, control valves, and their effect on jet collimation, a number of other problems need to be solved. For example, it is not obvious whether CMOS/VLSI materials can withstand the high pressures required for use in a compressed fluid printing process and that they can be useful for making micro-machined nozzles. Also, it is not obvious which materials and methods may provide a leak-proof connection from the high-pressure source of the marking material to the micro-machined nozzles. Methods that work at macro-scale do not necessarily work at micro-scale because uniformity of material properties and distribution of mechanical forces during assembly become more exacting.
Another problem with printing using compressed fluid formulations is that some portion of the jetted marking material that is in the form of nanometer size particles, not Pico-liter sized droplets, may escape along with the effluent gas into the nearby environment and create a potential health hazard. The printing system should be designed to minimize or eliminate such exposure to operators. The collection of such materials is fundamentally different from other continuous ink jet systems where the Pico-liter sized droplets are collected in a gutter when they are not intended to go to the substrate for printing.
Furthermore, many marking materials have a limited solubility in the pure compressed fluids and that limits the scope of this technology. Using conventional solvents as co-solvents with compressed fluids can enhance the solubility. While spray coating technologies for conventional solvent containing compressed fluids are known, directed beam printing with such fluids is not reported.